This study is designed to strengthen the empirical basis for assessment, taxonomy, epidemiology, & prediction of child/adolescent psychopathology via a 3-year follow-up of a national sample of 4-16-year-olds assessed in a home interview survey. The survey employed the ACQ Behavior Checklist to obtain data from parents on syndromes identified in multivariate analyses of child/adolescent psychopathology. Data were also obtained on family composition, family mental disorders, SES, child care arrangements, & welfare support. The sample was drawn from 100 nationally representative sampling sites stratified to yield 1 nonreferred boy & girl of each age 4-16 in each site (N = 2600), plus those found to be referred for mental health services in the preceding year (N = 89). ACQs have also been obtained for 5,000 4-16-year-olds referred to 18 mental health services across the country, permitting comparisons between matched clinical & nonclinical samples. The 3-year follow-up is designed to: (1) test the stability of problems & competencies; (2) compare findings for each sex age group & identify groups showing exceptional change; (3) test ACQ problems, competencies, syndromes, & profiles as predictors of referral for mental health services, suicide attempts, & other signs of disturbance; (4) test the ACQ as a predictor of problems reported on the Youth Self-Report (YSR) administered at follow-up; (5) test family variables as predictors of disturbance & YSR scores; (6) advance the taxonomy of child/adolescent disorders by identifying syndromes, profiles, & correlates remaining stable over 3 years; (7) test the accuracy of quantitative versus probability scales for predicting pathological outcomes. The 3-year follow-up will provide unique tests of the prevalence, stability, course, & prediction of behavioral/emotional problems in a national sample of children & adolescents. It will also provide a basis for cross-national comparisons of specific findings and of statistical models for stability, change, and prediction in the development of psychopathology.